Firearms having a direct gas impingement system or an indirect gas impingement system are known. Direct gas impingement is a type of gas operation for a firearm that directs gas from a fired cartridge directly to the bolt carrier or slide assembly to cycle the action in the firearm. More specifically, in a direct gas impingement system, when the firearm is fired, the exhaust propellant gases from the fired cartridge are directed through a port at the end of the barrel and then channeled back to the bolt carrier and will strike, or impinge, the bolt carrier moving it rearward toward the buttstock and into a retracted position. The exhaust gases will then discharge out the ejection port on the side of the firearm near the buttstock. After discharge, the spring acting on the bolt carrier will move the bolt carrier back to the engaged position at the same time stripping or picking up another cartridge from the magazine and moving that cartridge into a battery position within the firearm's breech. Examples of direct gas impingement firearms include the AR-15, M4 and M16 style firearms.
There are several known disadvantages with a direct gas impingement system. As an example, one disadvantage is that the breech of the firearm becomes fouled more quickly. This is caused by solids and impurities from the high-temperature gas from the fired cartridge condensing as they cool and being deposited on the bolt face and primary operating mechanism. Thorough and frequent cleaning is required to ensure reliability and proper operation of the firearm's operating mechanism. The amount of fouling depends upon the firearm's design as well as the type of propellant powder used in the fired cartridge.
A further disadvantage of direct gas impingement systems is that combustion gases from the fired cartridge heat the bolt and bolt carrier as the firearm operates. This heating may alter the temper of metal parts, accelerating wear and decreasing the service life of the bolt, extractor, and extractor spring. Additionally, heat dries up the firearm's lubricant and makes the firearm's operating parts difficult to handle when clearing malfunctions. Heat can also melt the lacquer coatings of steel cartridge cases, gumming up parts. Moreover, thermal expansion in the firearm's action can result in loss of tolerances and consequent degradation in the firearm's accuracy.
Firearms having an indirect gas impingement system differ from the direct gas impingement system in that the exhaust gases do not directly act on the bolt carrier. Rather, the exhaust gases, after the firearm has been fired, act on and move a piston-type rod that, in turn, is operatively connected to the bolt carrier. The movement of the piston-type rod moves the bolt carrier rearward, or in the direction opposite to the fired bullet, and to a retracted position. Once the piston has traveled a certain distance, the remaining unused gas acting on the piston-type rod is discharged through a port on the firearm. A spring acting on the piston will then move the rod and accompanying bolt carrier forward, picking up a new cartridge, and moving that cartridge into the battery position.
In contrast to the direct gas impingement system, a benefit of the indirect gas impingement system is a higher level of reliability by running a cleaner and cooler firearm by moving the operation of the firearm from the upper receiver and bolt carrier to a gas block using a small diameter short stroke piston which does not require constant cleaning or lubrication like the direct gas impingement system does in order to ensure functionality.
There remains, however, a need in the art for an improved indirect gas impingement system for a firearm.